Improve tracing and billing correlation with provider metadata in responses

We now populate provider metadata for OpenAI Chat responses and surface it across key response and event objects. Completion ID, system fingerprint, and other model-specific fields are included on ModelResponse/Message and emitted in RunOutput and RunCompletedEvent. This gives teams reliable identifiers to correlate with provider logs and invoices, streamlining debugging, cost analysis, and auditability — without disrupting existing workflows.

Details

Access completion_id, system_fingerprint, and model_extra from response.provider_data or event payloads
Available in ModelResponse/Message, RunOutput, and RunCompletedEvent
Backward compatible and additive; no migration required

Who this is for: Platform, MLOps, and application teams that need faster root-cause analysis, precise cost attribution, and improved observability in production.